How Much Lumbar Lordosis does a Patient Need to Reach their Age-Adjusted Alignment Target? A Formulated Approach Predicting Successful Surgical Outcomes

Study Design: Retrospective cohort study. Objectives: Identify optimal lumbar lordosis in adult deformity correction to achieve age-adjusted targets and sustained alignment. Methods: Surgical adult spinal deformity patients reaching an age-adjusted ideal alignment at one year were identified. Multilinear regression analysis was used to identify the relationship between regional curvatures (LL and TK) that enabled achievement of a given global alignment (T1 pelvic angle, TPA) based on pelvic incidence (PI). Results: 347 patients out of 1048 available reached their age-adjusted TPA within 5° (60-year-old, 72% women, body mass index 29 ± 6.2). They had a significant improvement in all sagittal parameters (except PI) from pre-operative baseline to 1 year following surgery (P <.001). Multilinear regression predicting L1-S1 based on TK, TPA, and PI demonstrated excellent results (R2 =.85). Simplification of the coefficients of prediction combined with a conversion to an age-based formula led to the following: LL = PI - 0.3TK - 0.5Age + 10. Internal validation of the formula led to a mean error of −.4°, and an absolute error of 5.0°. Internal validation on patients with an age-adjusted alignment revealed similar accuracy across the entire age-adjusted TPA spectrum (ranges of LL errors: ME =.2° to 1.7°, AE = 4.0° to 5.3°). Conclusion: This study provides a simple guideline to identify the amount of LL needed to reach a given alignment (i.e., age-adjusted target) based on PI and associated TK. Implementation of this predictive formula during pre-operative surgical planning may help to reduce unexpected sub-optimal post-operative alignment outcomes.